Method and system for a wireless multi-hop relay network

ABSTRACT

In a wireless multi-hop relay network arranged in a tree topology, the base station and one or more relay stations are associated as a virtual base station (VBS). The base station and each relay station have a unique virtual base station identifier (VBS-ID) associated with the path defined by the base station and the one or more relay stations. a relay station in the branch uses its VBS-ID for communicating with an attached subscriber station (e.g. a mobile station) such that communications between the base station and subscriber station occur via the VBS. Subscriber station data communications are relayed between the base station and the one or more relay stations over the VBS via a tunnel connection. The VBS is autoconfigurable. Mobility for subscriber stations and relay stations is provided through reconfiguration of VBS&#39;s.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.13/159,914 entitled “METHOD AND SYSTEM FOR A WIRELESS MULTI-HOP RELAYNETWORK” to Wang et al. filed Jun. 14, 2011, which is a continuation ofU.S. patent application Ser. No. 11/678,142, filed on Feb. 23, 2007, nowU.S. Pat. No. 7,986,915, which claims the benefit of U.S. ProvisionalPatent Application No. 60/776,448, filed on Feb. 24, 2006, the entiretyof which applications are incorporated by reference herein.

RELATED APPLICATIONS

This application is related to commonly owned and co-pending U.S. patentapplication Ser. No. 11/478,719, filed on Jul. 3, 2006, titled “METHODAND SYSTEM FOR A WIRELESS MULTI-HOP RELAY NETWORK”, which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to wireless networking protocols and systems.

BACKGROUND

WiMAX, described in the IEEE 802.16 Wireless Metropolitan Area Network(MAN) standard (IEEE 802.16-2005), allows for high-speed wireless datatransmissions over long distances. The core components of an 802.16network are base stations (BS) and subscriber stations (SS). An SS maybe a mobile station (MS). The WiMAX network was originally designed as aPoint-to-Multipoint (PMP) architecture. The 802.16-2005 standard definesa connection-oriented mechanism for data flow between BS and MS. AConnection ID (CID) is defined to associate a data flow service with aconnection. CIDs are also used by MS's in PMP networks to tell whichdata bursts in a DL frame should be decoded and which should not.

WiMAX is now progressing to large scales and full mobility. In order toextend access coverage, optimize utilization of radio resources, andsupport flexible mobility, WiMAX is migrating from the one-hop PMParchitecture to a multi-tier PMP topology, referred to as MMR (MobileMulti-hop Relay). MMR is a tree-like relay architecture wherein a BS andSS may be separated by one or more relay stations (RS).

The MMR architecture presents new complications. MMR is different fromlegacy one-hop PMP access, where radio resources are allocated bycentralized control in the Base Station (BS). The multi-tier MMR mayrequire a distributed radio source allocation schema across BS and RS,or a hybrid schema of both centralized and distributed control. Thisdistributed or hybrid schema should provide a relay operation to forwardthe data frame Down Link (DL) and Up Link (UL) between a BS and MS's viathe RS's. Further, mobility functionality must be provided for MS's andRS' s, both inter-tree and intra-tree.

Use of CIDs in MMR networks becomes a critical issue. Current suggestedrelay solutions require all RS to acquire, store, and decode the MACPDUs in DL frames to get the CIDs of the MS for relay operation. As aresult, RS MAC PDU decoding consumes excessive resources and RSforwarding tables become very large and ultimately unmanageable.Furthermore, to execute a handover of an MS from one branch to anotherbranch of the MMR network, all the MS CIDs have to be transferred fromall RS along the old branch to all RS along the new branch, resulting invery inefficient MMR relay operation. New relay and mobility solutionsare required for 802.16 MMR networks in order to provide commerciallyreasonable efficiency and performance.

SUMMARY

The invention provides several solutions for the current issues in theMMR multi-hop architecture. Radio resource access is accompanied withtopology information and shared/dedicated radio resource allocationpolicy. The overall end-to-end relay control is done in a collaboratemanner among BS and RS. To accomodate large scale network size,efficient radio usage, and effective mobility management, the MMRnetwork is logically partitioned into virtual groups. Based on the radioaccess policy, various methods are used to define the virtual groupssuch as vertical partitioning within a single routing domain (i.e.,centralized), or horizontal partitioning within multiple routing domains(distributed), or hybrid of both.

Aspects of the invention apply to these virtual groups, including autoconfiguration of the groups, use of the groups for data relay over therelay stations in the MMR, and mobility of relay stations and subscriberstations within the MMR.

Accordingly, in a wireless multi-hop relay network arranged in a treetopology, the invention broadly applies to one or more relay stationscoupled to a base station along a single tree branch. The base stationand one or more relay stations are associated as a first virtual basestation (VBS). The base station and each relay station have a uniquevirtual base station identifier (VBS-ID) associated with the pathdefined by the base station and the one or more relay stations. The lastrelay station in the branch uses its VBS-ID for communicating with anattached subscriber station (e.g. a mobile station) such thatcommunications between the base station and subscriber station occur viathe first VBS.

According to a further aspect, the first VBS is further associated witha tunnel connection identifier (T-CID). The base station uses the T-CIDto relay subscriber station data communications between the base stationand the one or more relay stations.

In one implementation, the base station and relay stations each includea routing table. Each routing table includes one or more entriesincluding a VBS-ID, a path list associated with the VBS-ID, and a T-CIDassociated with the VBS.

Each RS in the VBS can use the routing table in support of data relayacross the MMR. Accordingly, an RS performs the following functions inresponse to receipt of a message from an upstream station in the VBS.The RS searches the relay station routing table for the received T-CID.If the received T-CID is not in the routing table, the RS drops themessage. If the received T-CID is in the routing table, and the T-CID isassociated with a VBS-ID that is associated with another relay station,then the RS forwards the message to the another relay station. If thereceived T-CID is in the routing table and the T-CID is associated witha subscriber station, then the RS removes the T-CID and forwards themessage to the subscriber station via a connection identifier associatedwith the subscriber station.

When the multi-hop relay network is an 802.16 network, a relay stationin a VBS performs the following functions as part of VBS auto discoveryin accordance with the invention. The RS receives a DL-MAP message fromthe base station.

If the relay station is not attached to an upstream station then the RSsends a range request message to the upstream station. The RS will thenreceive a range response message from the upstream station containing aunique VBS-ID for the relay station. The RS then exchanges DSx messageswith the upstream station to obtain a T-CID. The RS then updates therouting table with an entry including the VBS-ID and T-CID.

If the relay station is attached to an upstream station, then the RSreplaces the station identifier in the DL-MAP message with the VBS-IDfor the relay station, and forwards the DL-MAP message downstream.

The RS may further perform the following functions in furtherance ofauto discovery. The RS can receive a range request message from adownstream relay station. The RS would then receive a range responsemessage from an upstream station containing a unique VBS-ID for thedownstream relay station. The RS would next receive a DSx messages fromthe upstream station containing a T-CID for the downstream station. TheRS forwards the DSx message to the downstream station, and updates itsrouting table with the VBS-ID and T-CID for the downstream station.

In accordance with another aspect of the invention, VBS's are used infurtherance of intra-tree handover in an MMR. The handover occursbetween the first VBS and a second VBS.

Accordingly, the second VBS includes one or more relay stations coupledto the base station along a second tree branch. The base station and oneor more relay stations along the second tree branch associated as asecond VBS. The base station and each relay station associated with thesecond VBS having a unique VBS-ID. A handover procedure transferssubscriber station communications from the first VBS to the second VBS.A relay station in the second VBS uses its VBS-ID for communicating withthe transferred subscriber stations via the second VBS, so thatcommunications between the base station and subscriber station occur viathe second VBS instead of the first VBS.

According to an implementation of the handover, a base station sends anadvertisement message including a list of available VBS including thesecond VBS. The base station then receives a handover indication messagefrom a subscriber station indicating that subscriber stationcommunications are transferring to the second VBS. The base station thenupdates its routing table to indicate a VBS-ID and T-CID for the secondVBS to be used for communicating with the subscriber station. Each relaystation in the second VBS updates its routing tables to indicate theVBS-ID and associated T-CID to be used for communicating with thesubscriber station.

In accordance with another aspect of the invention, VBS's are used infurtherance of inter-tree handover in an MMR network. The handoveroccurs between the first VBS and a second VBS, wherein each VBS isheaded by a separate BS.

In this case, a second base station is coupled to one or more relaystations along a single tree branch subordinate to the second basestation, the second base station and one or more relay stationsassociated as a second VBS. A handover procedure is performed totransfer subscriber station communications from the first VBS to thesecond VBS. A relay station in the second branch uses its VBS-ID forcommunicating with the transferred subscriber station via the second VBSso that communications between the base station and subscriber stationoccur via the second VBS instead of the first VBS.

According to an implementation, in order to perform inter-tree handover,the first and second base stations exchanging their routing tables sothat VBS's in each base station can be advertised by the other. Theremaining procedure for handover is substantially similar to thatdescribed for the intra-tree case.

The invention further provides “virtual access points” (VAPs). VAPs aregroups of network elements arranged in a tree topology, for example ahead BS and multiple VAP RS's, or a head RS and multiple other VAP RS's.All the network elements in a VAP share the same radio resource. A VAPcan provide multiple radio links via its VAP RS's. A subscriber stationor relay station attached to the VAP can communicate with a VAP over anyone of the radio links in a manner transparent to the subscriber orrelay station.

In accordance with the invention, VAPs can form VBS's. For instance, afirst and second VAP can be associated as a first virtual base station,wherein the first and second VAPs each have a unique virtual basestation identifier (VBS-ID). A relay station in the second VAP uses theVBS-ID of the second VAP for communicating with a subscriber stationattached to the second VAP so that communications between the BS andsubscriber station occur via the first VBS.

In further accordance with the invention, the base station and all VAPrelay stations in the first VAP share the same radio resource, so thatthe first VAP provides multiple radio links via its VAP relay stations.The relay station in the second VAP is capable of communicating with thefirst VAP over any one of the radio links in a manner transparent to therelay station. Thus, communications over the first VBS can occurtransparently via one of multiple radio links between the VAPs.

Furthermore, the second VAP can provide multiple second radio links viathe VAP relay stations in the second VAP. The subscriber station canthen communicate with the second VAP over any one of the second radiolinks in a manner transparent to the subscriber station.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the attached drawings in which:

FIG. 1 is a schematic diagram of a prior art multi-hop relay network;

FIG. 2 is a schematic diagram of a multi-hop relay network employingvirtual base stations (VBS) in accordance with the invention;

FIG. 3 is a schematic diagram of a multi-hop relay network employingvirtual access points and VBS in accordance with the invention, using aglobal tunnel connection identifier (T-CID);

FIG. 4 is a routing table for the base station (BS) in the network ofFIG. 3;

FIG. 5 is a routing table for the relay station (RS) RS5 in the networkof FIG. 3;

FIG. 6 is a schematic diagram of a multi-hop relay network employingvirtual access points and VBS in accordance with the invention, usinglocal T-CIDs;

FIG. 7 is a schematic diagram of a multi-hop relay network employing VBSand further showing VBS paths;

FIG. 8 is a system level flow diagram of VBS creation, auto discovery,and tunnel relay functions according to the invention;

FIG. 9 is an example MMR branch showing VBS and VBS routing tables;

FIG. 10 is a representation of a TLV extension for an 802.16 REG-RSPmessage;

FIG. 11 is a representation of a TLV extension for an 802.16 DSA-REQmessage;

FIG. 12 is a flow chart showing RS processing of a DSA-REQ message aspart of the VBS auto discovery process in accordance with the invention;

FIG. 13 is a working flow diagram showing VBS auto discovery;

FIG. 14 is a continuation of the working flow diagram of FIG. 13;

FIG. 15 is a schematic diagram of an MMR network showing intra-BS andinter-BS handover functions;

FIG. 16 is a system level flow diagram of MMR mobility in accordancewith the invention;

FIG. 17 is a schematic diagram of an MMR network wherein a mobilestation (MS) moves from a BS to an RS;

FIG. 18 is a working flow diagram of the message exchanges supportingthe MS mobility of FIG. 17;

FIG. 19 is a schematic diagram of an MMR network wherein an MS movesfrom an RS to a BS;

FIG. 20 is a working flow diagram of the message exchanges supportingthe MS mobility of FIG. 19;

FIG. 21 is a schematic diagram of two MMR trees wherein an MS moves froma BS in one tree to an RS in another tree;

FIG. 22 is a working flow diagram of the message exchanges supportingthe MS mobility of FIG. 21;

FIG. 23 is a schematic diagram of an MMR network wherein an RS movesfrom one branch of an MMR tree to another branch of the MMR tree;

FIG. 24A is a working flow diagram of the message exchanges supportingthe RS mobility of FIG. 23;

FIG. 24B is a continuation of the working flow diagram of FIG. 24A;

FIG. 25 is a schematic diagram of two MMR trees wherein an RS moves froman RS of one MMR tree to a BS of another MMR tree;

FIG. 26A is a working flow diagram of the message exchanges supportingthe RS mobility of FIG. 21; and

FIG. 26B is a continuation of the working flow diagram of FIG. 26A.

DETAILED DESCRIPTION

A wireless multi-hop relay access network is described herein. In amulti-hop relay access network, relay stations (RS) are introduced forfixed, nomadic and mobile relay usage between base stations (BS) andsubscriber stations (SS). The functional scope of a relay station canscale from being very simple such as an analog signal repeater, to abase station compliant fully functional device capable of radio resourcescheduling, security authentication and connection management for mobilestations, in case a base station fails.

FIG. 1 is a schematic diagram of a very simple two-tier PMP relaynetwork. In this example, the SS are mobile stations (MS). MS is usedfor the remainder of this description, as the invention providesadvantages when used with mobile stations, though it is understood thatmobile stations are a subset of subscriber stations to which theinvention broadly applies. At the tree trunk level, BS 60 communicateswith RS 62 and RS 63. RS 62 in turn communicates with MS 65 and MS 66.Similarly, RS 63 communicates with RS 67 and RS 68. RS 67 communicateswith MS 69, and RS 68 communicates with MS 70.

Through the use of a PMP multi-hop relay protocol, a payload can, forexample, be delivered from BS 60 to SS 69 through RS 63 and RS 67. FIG.2 is only one example of a PMP multi-hop relay network that can be usedwith the present invention. It is to be understood that the number ofRS's and MS's in the network can vary from that shown in FIG. 2. Theexample of FIG. 2 is a tree topology, and this is assumed for thedetails that follow. In an 802.16 network, this PMP multi-hop relaynetwork is referred to as MMR (Multiple Multi-hop Relay). The variousaspects of the invention will be described as applied to an 802.16 MMRnetwork. The messaging protocols of 802.16 will be referred to hereinand are fully described in “IEEE Std 802.16e 2005”, which is anextenstion of “IEEE Std 802.16 2004”, all available from the IEEEStandards Association, and herein incorporated by reference.

In an 802.16 MMR network like that of FIG. 1 several functional aspectsmust be addressed. There must be provided a means for relaying databetween BS and MS via the RS's. There must also be provided a means formaintaining data connections between the BS and MS when the MS or anyRS' s on the path between it and the BS move. In accordance with theinvention, the concept of a virtual base station (VBS) is introduced toprovide these and other functions in an efficient and high performancemanner. Referring to FIG. 2, there is shown the MMR network of FIG. 1wherein VBS are employed. A VBS is an MMR logical partition of the BSand RS' s along an MMR path running between a BS and MS or RS. SeveralVBS are shown in FIG. 2. VBS1 consists of a partition of the BS 60, RS63, and RS 68. From the perspective of the MS 70, VBS 1 is functionallyequivalent to a BS to which it is directly connected. But data isactually relayed between the BS 60 and MS 70 via the RS 63 and 68. VBS2is shown consisting of a partition of the BS 60, RS 63, and RS 67. TheMS 69 communicates with VBS2 as if it is a directly attached BS. VBS3 isshown consisting of a partition of the BS 60 and RS 62. The MS 65 and 66communicate with VBS3 as if it is a directly attached BS.

Various aspects of the invention are now described in detail, asfollows:

Virtual Access Point

Autodiscovery and Data Relay over VBS

Mobility

Inter-tree and intra-tree MS mobility

Inter-tree and intra-tree RS mobility

Virtual Access Point

In accordance with an aspect of the invention, a “virtual access point”(VAP) is defined. A VAP, also referred to as a “cell”, is a group ofnetwork elements such as BS and RS, or all RS. The network elements ineach cell are arranged in a tree topology. A single VAP appears toexternal network elements as a single BS which may have one or moreradio links for attachment.

Referring to FIG. 3, a topological view of a network implementing VAPsis shown. Each VAP consists of one cell head (BS or RS) and all of itssubordinate RS. As shown, VAP 1 (100) includes cell head BS (102) andRS1 (104), RS2 (106), RS3 (108), and RS4 (110). VAP 2 (120) includescell head RS5 (122), RS6 (124), RS7 (126), and RS8 (128). VAP 3 (130)includes cell head RS9 (132), RS10 (134), RS11 (136), and RS12 (138). AnMS 140 is shown attached to the VAP 2. Within each VAP, all the nodesshare the same network resources including geographical topologyinformation, radio resource information such as preamble, channel andassociated control/data information (e.g., 802.16 DL-MAP_IE, data packetflow SFIDs). So, from any MS's perspective, the VAP to which it isattached is no different than a BS as previously defined for an 802.16network.

In FIG. 3, the MS 140 is shown to have multiple access links 150, 152 tothe VAP 2. All these links have the same attributes (preamble, channel,DL-MAP_IE, etc,.). So the mobility for an MS within a VAP is the same asthe 802.16 defined process by which an access link is chosen by the BSbased on link quality (see 802.16 standard.) The MS can be switchedbetween these access links in a manner that is transparent to the MS. Infurther accordance with the invention, the 802.16 handover process onlyhappens between VAPs, in the same manner in which an MS roams betweenthe serving BS and the target BS in a traditional 802.16 PMP network.Thus, the 802.16 handover process would be invoked if MS 140 moves toVAP 3 (shown as arrow 154).

The VAPs of FIG. 3 cooperate to provide a VBS for communication with theMS 140 as will be further described. An implementation of a VBS (156) isshown in FIG. 3 as a partition of VAP 1 concatenated with a partition ofVAP2. In order to support the VBS functionality, the cell head for eachVAP has associated with it a VBS routing table. The BS has a VBS routingtable 160. The RS5 has a VBS routing table 162. Examples of VBS routingtables are shown in FIGS. 4 and 5. The table 160 has entries 160 a forVBS paths through the VAPs. Column 160 b stores a VBS Identifier(VBS-ID). Column 160 c stores a path list with which the VBS-ID isassociated. Column 160 d is the intra-cell next hop for the path list.Column 160 e is the inter-cell next hop for the path list. Columns 160 fand 160 g are ingress ports and egress ports respectively for this path.Column 160 h is the endpoint (RS or MS) of the path. Column 160 i is aT-CID related to the path for the entry. The table 162 has similarentries and columns labelled 162 a-i.

In FIG. 3, the BS 102 of VAP 1 may have a 3 sector antenna. One Oncesector is directed to RS1, and the second one to RS4. Each antenna is anidentified air interface. The routing paths in the VAP 1 are thusBS→RS1→RS2, BS→RS1→RS3, and BS→RS4. The BS 102 can send the same databurst to RS2, RS3 and RS4. The internal relay RS1 has its own routingtable to forward the data to RS2 and RS3.

RS5 also has a 3 sector antenna in this example. One, antenna #4, is theingress sector to RS5 from VBS1. Another, antenna #5, is directed toRS6, while the other, antenna #6, is directed to RS8. The potentialrouting paths from the BS 102 to the MS 140 are: BS→RS1→R52→R55→R57,BS→RS1→R53→R55→R57, BS→R54→R55→R57, BS→RS1→R52→R55→R58,BS→RS1→R53→R55→R58, BS→R54→R55→R58, which are the combination of all thepossible paths in the VAP 1 concatenated with all possible paths in theVAP 2. The determination of the routing path at a given time depends onwhich air link is used in between VAP 1 and VAP 2. Note that the BS 102in VAP 1 may not see RS6 (which is a local topologically to VAP 2, thusnot externally visible), but BS 102 can see RS5, RS7, and RS8, as theserelay stations define the boundaries of the VAP.

Referring again to FIGS. 4 and 5, the contents of the virtual routingtable 160 for BS 102 (VAP 1 cell head) and table 162 for RS5 (122) (VAP2 cell head) are shown one example. In this example, the BS 102dynamically assigns the path R52→R53→R54 via antenna #1 as the accesslink to RS5 (of VAP2), based on the measured air link quality (obtainedas feedback from RS5). The RS5 dynamically assigns the path R55→R56→R57via antenna #5 as the access link to MS1. The path from BS to MS1 isthus BS→RS1→R52→R55→R56→R57, and this is the path currently used as theVBS.

In the virtual routing table 160 for the BS, shown in FIG. 4, twoentries exist; one for the path currently attached to RS5, and one forthe path to MS 140. The first entry 160 a has VBS-ID VBS0, path list(BS, RS1, RS2), and intra cell next hop RS1. There is no inter cell hopor ingress port for this link. The egress port for this path is antenna#1 of the three sectors. RS5 is the endpoint attachment. The secondentry traces the path from BS to the endpoint MS as seen from theperspective of the BS. This entry has VBS-ID VBS1, path list (BS, RS1,RS2, RS5, RS7). The intra cell next is hop RS1, the inter cell next hopis RS5, and the egress port is antenna #1. This path ultimately ends atthe MS.

The virtual routing table 162 for RS5 includes one entry 162 a tracingthe currently selected path from the BS in VAP 1 to the MS attached toVAP 2 as seen from the perspective of the RS5. Thus the path entry 162 ais BS→RS1→RS2→R55→RS6→RS7. The path is assigned VBS-ID VBS1. The intracell next hop for RS5 is RS6. The inter cell next hop is the MS1. Theingress port is antenna #4 (from RS2), and the egress port in antenna #5(to RS6). It is thus seen that the VBS “VBS1” describes the VBS asoutlined in FIG. 3. Depending on which air links are enabled, data willbe relayed from BS to RS5 and on to the MS, while the MS communicatesusing VBS identifier VBS1 as if it were communicating with BS 102, whenit is actually communicating with RS7.

In other words, one can see that the end-to-end data relay from the BSto the MS involves a virtual BS, named VBS1, which in turn is apartition of two VAPs (VAP1 and VAP2). It requires collaboration betweenthe BS and RS5, which are the VAP1 and VAP2 cell head nodesrespectively, to provide the collective topology management and theassociated radio resource allocation. For example, in FIG. 4 and FIG. 5,the tunnel CID T-CID1 represents this collaborative relationship betweenVAP1 and VAP2.

The mobility of RS5 via the various air links to/from RS2, RS3, and RS4is chosen by the BS and is thus transparent to RS5. Likewise, themobility of MS via the air links to/from RS7 and RS8 is chosen by RS5and is thus transparent to MS. As the link quality of the various linkschanges, the RS5 and/or the MS will transparently move between the airlinks, and the virtual routing tables for BS x and RS5 will be updatedaccordingly. Meanwhile the MS continues to communicate via VBS1. Thehandover functionality of 802.16 needs only be implemented between VAPs,for instance between VAP 2 and VAP 3 (as indicated by arrow 154).

In FIG. 3, the collective topology management and the associated radioresource allocation between VAP1 and VAP2 is represented by a globaltunnel CID T-CID1. That is, T-CID1 is recognized as a unique T-CID byboth VAP1 and VAP2. Alternatively, as shown in FIG. 6, local T-CIDs maybe employed. In this case, the end-to-end data relay occurs via twoT-CIDs, herein shown as T-CID1 and T-CID2. T-CID one is used to tunneldata between BS of VAP1 and RS5 of VAP2. T-CID2 is used to tunnel databetween RS5 of VAP2 and RS7 of VAP2. In FIG. 5, the VBS routing tablefor RS5 would include the tunnel CID T-CID2 instead of T-CID1. Duringend-to -end data relay, a tunnel CID swapping mechanism manages theswitching of T-CID information. See co-pending U.S. Patent ApplicationPublication No. 2007/0072604 to Wang, which is incorporated by referencefor further details regarding this swapping mechanism.

It is now noted that, if the subordinate relay stations within the VAPs1 and 2 of FIG. 3 are not present, the VAPs collapse to the simpler caseof a BS and RS in a tree topology, as was shown in FIGS. 1 and 2. Inthis case, Inter-cell hop and port information is not required in theVBS routing tables. For clarity of description, this simpler model ofthe MMR network will be used in the following examples.

Auto discovery and Data Relay

In accordance with the invention, the cell head for a given MMR tree iscapable of automatically ascertaining the topology of the MMR treesubordinate to it, and automatically creates VBS's appropriate for thistopology. This is referred to herein as “auto discovery”. Furthermore,once auto discovery is complete, data can be relayed from a source,across the nodes of the VBS, to a destination. This process is referredto as “VBS relay”.

Referring to FIG. 6, VBSs' are defined as follows. First of all, everyBS is a VBS. Then, if an RS is attached to a VBS, the combination of theVBS and RS is a new VBS. Each VBS can thus be represented by a path listwhich is a branch of the MMR tree. Thus, the total number of VBS isproportional to the total number of RS in an MMR tree. As can be seen inFIG. 6, an MMR tree is shown. BS 200 is the root of the tree. RS1 (202)is attached to the BS 200. RS 2 (204) is also attached to BS 200. RS 3(206) is attached to RS2. There are four VBS defined for this MMR tree.The BS 200 at the root of the MMR tree is VBS1. MS1 (208) is attached toVBS1. VBS2 is defined as (BS, RS1). MS2 (210) is attached to VBS2. VBS3is defined as (BS, RS2). VBS4 is defined as (BS, RS2, RS3). MS3 (212) isattached to VBS4.

Mechanisms are provided for VBS topology auto discovery and subsequentVBS relay. The high level MMR system behaviour for VBS relay is shown inFIG. 7. Further detail regarding the “Tunnel CID” or “T-CID” referred tohereinafter is can be found in co-pending U.S. patent application Ser.No. 11/478,719, titled “Method and System for a Wireless Multi-Hop RelayNetwork”, incorporated fully by reference herein. First, an RS attachesto a BS in the MMR tree (300). A VBS topology auto discovery processthen occurs as will be further described (302). The BS allocates aVBS-ID and T-CID for the RS (306) and stores it in its VBS routingtable. The RS adds the VBS ID and Tunnel CID information in its VBStable (308). The process continues for each RS along the branch.Finally, an MS attaches to the last RS in an MMR tree branch (310). TheBS adds the MS to the VBS routing table (312), and the tunnel CID relaybetween the MS and BS can commence (314).

This process will be described as it applies to the example branch of anMMR tree of FIG. 8 and the working flow diagrams of FIGS. 9 and 10. InFIG. 8, a BS 400 is coupled to an RS1 402, which is further coupled toan RS2 404. In order to implement the VBS functionality, each BS and RSincludes a VBS controller function element as shown in FIG. 8. The BSincludes VBS controller 406. The RS1 includes VBS controller 408. TheRS2 includes VBS controller 410. Each VBS controller creates andmaintains a VBS routing table that includes all routing paths from thisnode (BS or RS) to all the nodes in its subordinate tree. In thisexample the BS includes VBS routing table 412. The RS1 includes VBSrouting table 414. The RS2 includes VBS routing table 416. Each routingpath entry includes a VBS-ID, a path list, a T-CID. The routing tableentry associated with the last RS in the branch also includes anendpoint ID. In FIG. 8, each VBS routing table is shown with itscontents after autoconfiguration is complete. Each VBS routing table412, 414, 416 is created and maintained by using a BS-oriented sourcerouting protocol (pending U.S. patent application Ser. No. 11/478,719),and the signalling messages as currently defined in 802.16(802.16e-2005)—that is, no new messages are required to implement theinvention. In particular, the VBS routing tables are created through useof DL-MAP, RNG-REQ, RNG-RSP, and DSAx messages. New TLVs are defined forthese messages to include an explicit route, which is a path listconsisting of the relay node IDs in a VBS.

Auto discovery operates generally as follows. The BS periodicallybroadcasts the cell preamble and DL-MAP to all subordinate trees.Initially, the DL-MAP contains the BS-ID as the initial node along thebranch. When each attached RS that has already entered the networkreceives the DL-MAP, it replaces the BS-ID field in the DL-MAP with itsVBS ID and further broadcasts DL-MAP to its subordinate tree. When a new(unattached) RS receives the DL-MAP, it copies the received VBS ID(which is that associated with the RS from which it received the DL-MAP(“access RS”)) into a RNG-REQ message and sends it back to the BS. Alongthe backward direction, each receiving RS forwards RNG-REQ upstream.Eventually the BS receives the RNG-REQ message. Based on pre-learnedtopology and the VBS ID from the access RS, the BS creates a new pathentry and VBS ID for the newly attached RS in its routing table, andissues a RNG-RSP message containing the new VBS-ID to the new RS tofinish the network entry operation for this new RS. This RNG-RSP messageis tunnelled to the designated access RS (i.e. the RS designated in theRNG-REQ) via the T-CID previously allocated to the designated access RS.In turn, the access RS forwards the RNG-RSP message downstream to thenew RS. Once the entry stage for the new RS is complete, the BS sends aDSA-REQ (Dynamic Service Add) message with the new created path in theexplicit route TLV to configure T-CID for the new RS. DSA messages arenot tunnelled. Each RS along the way checks destination RS' s node IDand the explicit route TLV carried by the DSA message to see if it selfis in the explicit route and if the path is a new path. If not, the RSjust simply drops this message. Otherwise, the RS creates a new entry inits VBS routing table to store the new routing path list, VBS ID, andthe T-CID associated with the searched entry for relay purposes. The RSthen further sends the DSA message to the subordinate tree. Eventuallyall the RS along the branch acquire the new path, new VBS ID and theT-CID and store it in their VBS routing tables.

Up to this point, the MMR network has created the overall VBSarchitecture and T-CID paths. Now, when an MS attaches to an RS, itfirst receives a cell preamble and DL-MAP message containing the accessRS's VBS ID, and sends an initial RNG-REQ message to begin the networkentry process. The RS attached to the MS copies the VBS ID from its VBSrouting table into the RNG-REQ message and relays it back to the BS.Based on the VBS ID, now the BS has the knowledge of what T-CID shouldbe used to deliver data bursts to the MS. When the BS sends the databursts to the target MS, it builds normal DL-MAP-IE messages with anadded T-CID. Now the RS participate in the VBS relay operation. Each RSmerely decodes DL-MAP-IE to the T-CID. By checking the VBS routingtable, the RS determines if it should further relay the burst down thetree or simply drop it. Eventually the last access RS receives the DLframe, decodes the DL-MAP and the data burst to get MS CID, and forwardseach MS's MAC PDU downstream. In accordance with an advantage of theinvention, each intermediate RS along the BS-MS MMR path need only checkthe T-CID to relay the DL frame. There is no need to decode the databurst to check the MS MAC address to forward the packet.

In accordance with an implementation of the invention, the RNG-RSP andDSA-REQ signalling messages used in the above described process utilizenew TLVs in accordance with the invention. In FIG. 10 there is shown aVBS-ID TLV 420, having syntax “VBS_ID” (422) and length 24 bits (424).The TLV list for the 802.16 RNG-RSP message is extended to include thisTLV. It is used by the BS to convey a new VBS-ID to an RS. In FIG. 11there is shown an explicit route TLV 430. This TLV is used by the BS toconvey a path list associated with a VBS to an RS in a DSA-REQ message.A first entry 432 represents the number of entries in the list (434) andhas a size of 16 bits (436). It is followed by an entry 438 includingthe list of CIDs (each size 16 bits, 440) for each node (i.e. RS) in theVBS path.

Further detail as to how an RS processes a DSA-REQ message having anexplicit route TLV is shown in the flow chart of FIG. 12. Upon receiptof a DSA-REQ message (450), the RS checks to see if its own CID, denotedherein as RS-ID, is in the explicit route list (452). If it is not, thenthe message is destined for a node that is not in a VBS containing anyRS subordinate tree. Therefore the message is dropped (454). If it is inthe list, the RS then checks to see if its RS-ID is in the generic MACheader—i.e. is this MAC PDU addressed to this RS? (456). If not, thismeans the message is directed to a downstream RS that is part of a VBSassociated with this RS. So the RS updates its routing table with theVBS-ID, path list, ant T-CID for the destination RS and forwards theDSA-REQ to the next hop RS (458). If the RS-ID is found in the genericheader, then the RS checks to see if it is the last hop in the explicitroute (462). If it is the last hop, it updates its routing table withits VBS-ID, path list and T-CID (464), and sends a DSA-RSP message backto the BS (466). If it is not the last hop, this means the explicit pathis crossing a VAP boundary into a new VAP with new CIDs and T-CIDs. Inthis case it adds new CIDs, T-CID, and path information in the DSA-REQ(468). It then establishes a mapping between the old and new CIDs (470).Then the RS updates its routing table with the VBS-ID, T-CID and pathinformation (472), and forwards the DSA-REQ to the next hop in the newVAP (474).

The auto configuration process is now shown in detail with reference tothe working flow diagrams of FIGS. 13 and 14. In this example, the BS400, RS1 402, and RS2 404 serve as a VBS and tunnel relay for an MS.Each VBS table is shown as it is progressively built by referencenumbers 412 a-n, 414 a-n, 416 a-n. Before any RS are attached, the BSrecognizes itself as a VBS, as indicated by path list VBS0={BS} in table412 a. The process begins when the BS broadcasts a DL_MAP message (500).This DL-MAP message contains the VBS0 (as indicated by DL-MAP(VBS0)).The RS1 (that has not yet entered the network) receives the DL_MAPmessage from the BS, and sends a RNG-REQ message including itself andVBS0 (as indicated by RNG-REQ(VBS0,RS1) (502). The BS then builds a newentry in its VBS routing table associating VBS1 with (BS, RS1) (412 b).The BS then sends a RNG-RSP message back to the RS1 (504). This RNG-RSPmessage includes the assigned VBS-ID VBS1. RS1 builds a VBS routingtable which includes an entry for VBS1. Now RS1 performs the 802.16entry process for attaching to the BS (506). The BS now selects a tunnelCID that will be used for VBS relay via RS 1. The BS updates its routingtable entry for VBS1 to associate VBS1 with T-CID1 (412 c). The BS thensends a DSA request containing the new explicit route (BS, RS1) andT-CID for VBS1, i.e. T-CID1, to RS1 (508). RS1 updates its VBS routingtable entry for VBS1 with the new route and tunnel CID T-CID 1 (414 a),and then sends a DSA-RSP message back to the BS (510), completing theRS1 entry process.

The BS now sends another DL-MAP(VBS0) message (512). The attached RS1which has completed the entry process forwards the DL-MAP messagedownstream with its VBS-ID VBS1 (514). The RS2 receives the DL-MAP(VBS1)message from the RS1, in the same manner that it would receive a DL-MAPmessage from a BS. The RS2 then begins the entry process by sending aRNG-REQ message identifying VBS1 and RS2 (itself) (516). When RS1receives the RNG-REQ message, it forwards it to the BS (518). The BSproduces a new entry for its VBS routing table associating a new VBS-IDVBS2 with the path (VBS1,RS2) (412 d). The BS issues a RNG-RSP messagewith the VBS2 information (RNG-RSP(VBS2,RS2) (520) and tunnels thismessage using TCID-1. RS1 receives and un-tunnels the RNG-RSP message.RS1 builds a new entry for VBS2 in its VBS routing table. The RNG-RSP(VBS2,RS2) message is then forwarded on to RS2 (522). RS2 updates itsVBS routing table with an entry for VBS2 and completes the entry process(524). The BS now selects a tunnel CID that will be used for VBS2. TheBS updates the VBS routing table to associate VBS2 with T-CID2 (412 e).The BS then sends a DSA request containing the new explicit route (VBS1,RS2) and tunnel CID T-CID2 for VBS2 (526). RS1 updates its VBS routingtable entry for VBS2 with the new route (VBS1,RS2) and tunnel CID T-CID2(414 b), and sends the DSA-REQ(T-CID2) message downstream to RS2 (528).RS2 updates its VBS routing table to associate VBS2 with new route(VBS1, RS2) and tunnel CID T-CID2 (416 b). A DSA-RSP(T-CID2) message isreturned to RS1, and then to the BS (530, 532).

The BS then issues another DL-MAP (VBS0) message (534). RS1 in turnsends a DL-MAP(VBS1) message downstream (536). RS2 receives the DL-MAP(VBS1) and sends a DL-MAP(VBS2) message downstream (538). An MS receivesthis message. The MS now interacts with VBS2 just as it would with a BSin a single hop PMP network. The MS begins the network entry process bysending a RNG-REQ message to the source of the DL-MAP—that is, MS sendsa RNG-REQ(VBS2, MS) message (540). This RNG-REQ(VBS2,MS) message is sentup the tree to the BS via the T-CID associated with VBS2—i.e. TCID2(542, 544). The BS finds the VBS2 entry in its VBS routing table andupdates it by adding MS to the path list (412 f). The BS then issues aRNG-RSP(VBS2, MS) message (546) via tunnel TCID2. By checking therouting table, RS1 transparently relay RNG-RSP to RS2 (414 e, 548). RS2un-tunnel the received message, updates its VBS2 path entries to includeMS (416 b), and relay the RNG-RSP message (550). The MS then receivesthe RNG-RSP(VBS2,MS) message. The MS entry process and connectionestablishment now occurs between the BS and MS (552). Note that the MSknows of communications only with VBS2. But VBS2 is associated withT-CID2, so all communications between BS and MS are relayed via RS1 andRS2 over the T-CID2 connection. Once the MS connection is established,the BS sends DL frames containing DL_MAP_IE for the MS-CID, and databursts for the MS-CID, encapsulated in the T-CID2 (554). The relaystation RS1 decodes the DL_MAP and looks up the TCID2 in its routingtable (556) and relays the DL frame down the VBS2 path to RS2 (558). TheRS2 decodes the DL-MAP and looks up T-CID 2 in its routing table (560)and sees that it is the endpoint for T-CID2, so it de-encapsulates theDL frame and sends it on to the MS (562). The MS then decodes theDL-MAP-IE for its MS CID in the normal 802.16 manner.

In accordance with one advantage of the invention, each RS along the MMRpath need only check the T-CID to relay the DL frame. There is no needto decode the data burst to check the MS MAC address to forward thepacket. In large trees where RS are associated with many MS, the T-CIDrelay offers significant efficiencies.

Mobility

In a wireless multi-hop relay access network such as that of FIG. 1, amobile subscriber station (MS) may move within the network. Forinstance, a laptop or PDA may be carried by its user from one locationin the network to another. The MMR nework maintains network connectivitywith the MS by adjusting the manner in with the MS accesses the network.When an MS is attached to a particular BS or RS, it may move a shortdistance, in which case transmission power adjustments and advance timeadjustments can be made to accommodate the movement. Or, the MS may moveso far from the BS or RS that it must transition to use a differentradio link to the BS or RS. (e.g. FIG. 3 “x”). Or, the MS may move sofar from the BS or RS that a “handover” must occur from the BS or RSsuch that network access is now provided by a different BS or RS. Inaddition, an RS in the network may also be a mobile device. As such, itmay move just as described above with regard to the MS, and MS and RSmay be mobile simultaneously.

In accordance with the invention, MS and RS mobility may occur within anMMR network in the same manner that MS mobility is handled in a PMP802.16 network, except that handover occurs between VBS rather than BS.In FIG. 11, a BS BS1 (600) is shown having two subordinate VBS, VBS1(602) and VBS2 (604). And handover of an MS (606) from VBS1 to VBS2would be an intra-tree handover, controlled by the VBS controller 607 inthe BS 1. Another BS BS2 (608) has a subordinate VBS VBS3 (610). Ahandover of an MS (612) from VBS3 to VBS2 would be an inter-treehandover. This handover would be controlled by the VBS controller 613 inBS2 and would involve a handover controller 614 in the ASN gateway 616that connects the BS1 and BS2.

The general MMR system mobility behaviour is shown in FIG. 15. A BSperiodically broadcasts all its neighbouring VBS information (bothintra-tree and inter-tree) (700). The BS directs an MS or RS to startits scan process with a given recommended VBS list (702). The MS or RSdetermines a target VBS from the received list (704). A handover thenoccurs from the serving VBS to the target VBS (706). If an RS is moving,a new VBS and T-CID may be created (708). A context switch occurs fromthe serving to target VBS (710). If a MS is moving inter-tree, the MS'sCID may be replaced (712). Finally, a new tunnel CID relay commences(714).

MS Mobility

Referring now to FIG. 17, there is shown an MS 800 that moves intra-treefrom a serving BS 802 to a target RS 804. The topology of FIG. 3includes two VBSs-VBS0 (BS), and VBS1 (BS, RS1). The MS is initiallyattached to the BS, and is moving to RS1. The current serving VBS isVBS0. The target VBS is VBS1. The working flow diagram for this handoveris shown in FIG. 18. Initially, the virtual routing table 810 a for BSincludes the path for VBS0 (BS), and the path for VBS1 (BS, RS1). Thepath for VBS1 is associated with a tunnel CID T-CID1. The virtualrouting table 812 a for RS1 includes the path for VBS1 and T-CID1. TheMS is shown attached to the BS (814 a). DL-MAP and data bursts areexchanged directly between the BS and MS via the MS' CID. The currentserving VBS, VBS0, broadcasts an MOB_NBR-ADV message to the MS inaccordance with 802.16 (820). The MOB_NBR-ADV message includes VBS-IDsrecommended for handover—in this case, VBS1. The MS starts its scanprocess with the recommended VBS list in the advertisement message.Meanwhile, the MS receives a preamble and DL-MAP message from the RS1including the VBS-ID VBS1 (828). The MS sends an HO request message tothe serving VBS (i.e. BS) including the chosen target VBS1, and the BSsends an HO response back (824). The MS uses the new VBS1 for initialranging. RNG-REQ and RNG-RSP messages are relayed from MS to BS viaT-CID1 (830, 832, 834). The BS now associates the MS with VBS1 in itsrouting table (810 b). VBS1 is now the target VBS. RS1's routing tableis updated to include MS as its endpoint (812 b). The MS is now attachedto VBS1 (814 b). The MS now sends an MOB-HO_IND message to the severingcurrent VBS (i.e. BS) (836). The BS redirects all data flow for the MSto the target VBS1 by putting the VBS1's T-CID in the DL-MAP (838). VBS1now relays data bursts to the MS (840).

In FIG. 19, the same MMR tree is shown, but this time the MS 800 movesintra-tree from serving VBS1 to target VBS0. The MS is initiallyattached to RS1, and is moving to BS. The current serving VBS is VBS1(BS, RS1). The working flow for this handover is shown in FIG. 20.Initially, the virtual routing table 910 for the BS includes the pathfor VBS0 (BS), and the path for VBS1 (BS, RS1). The path for VBS1 isassociated with a tunnel CID T-CID1 and the endpoint MS. The virtualrouting table 912 a for RS1 includes the path for VBS1 (BS, RS1), thetunnel CID T-CID1, and the endpoint MS. Prior to handover, data burstsare relayed via T-CID1 between BS and MS (920, 922). Then, the BSbroadcasts an MOB_NBR-ADV message (924), which is broadcast by thedownstream VBS1 (926). The MOB_NBR-ADV message includes a list ofVBS-IDs recommended for handover—in this case, VBS0. The MS starts itsscan process with the recommended VBS list in the advertisement message.The MS exchanges HO request and HO response messages with the servingVBS VBS1 including the chosen target VBS0 (928). Meanwhile, the MSreceives a preamble and DL-MAP message from the BS including the VBS-IDVBS0 (930). The MS uses the new VBS0 for initial ranging, exchangingRNG-REQ and RNG-RSP messages with VBS0 (932,934). The BS now associatesthe MS with VBS0 in its routing table (910 b). RS1's routing table isupdated to remove the MS as the VBS1 endpoint (912 b). The MS now sendsan MOB-HO_IND message to the severing current VBS1 (936), which sends iton to its root BS (938). The VBS 1 BS redirects all data flow for the MSto the target VBS0 by sending data bursts over VBS0, i.e. directly tothe MS (940).

In FIG. 21, two MMR trees are shown. BS1 (1000) is the root of one tree.BS2 (1002) is the root of a second tree. RS1 (1004) is subordinate toBS2. There are three VBSs-VBS0 (BS1), VBS1 (BS2), and VBS2 (VBS1, RS1).An MS 1006 moves inter-tree from BS1 to RS1.

The working flow diagram for this handover is shown in FIG. 22. Prior tohandover, the VBS routing table 1008 a for BS1 includes the path forVBS0 (BS1), and associates this path with the endpoint MS. The VBSrouting table 1010 a for BS2 includes the VBS1 path (BS2), and the VBS2path (VBS1, RS1) and it's associated T-CID1. The VBS routing table 1012a for RS1 includes the path for VBS2 (VBS1, RS1), and the tunnel CIDT-CID1. Prior to handover, DL-MAP and data bursts are exchanged directlybetween BS1 and MS (1014). Also prior to handover, BS1 and BS2 exchangetheir VBS routing tables (1016). BS1 now broadcasts an MOB_NBR-ADVmessage to the MS (1018). The MOB_NBR-ADV message includes VBS-IDs fromboth trees recommended for handover—in this case, VBS1 and VBS2. The MSstarts its scan process with the recommended VBS list in theadvertisement message. HO request and response messages are exchangedbetween the MS and the serving VBS0 (1020). The MS uses the new VBS2 forinitial ranging. RNG-REQ and RNG-RSP messages are relayed between the MSand BS2 via the T-CID1 (1022, 1024, 1026, 1028). The BS2 now associatesthe MS with VBS2 in its routing table (1010 b). RS1's routing table isupdated to add the MS as its endpoint (1012 b). The MS, now attached toVBS2 (as indicated by 1030) now sends an MOB-HO_IND message to thesevering current VBS0 (1032). The BS2 redirects all data flow for the MSto the target VBS2 by sending DL-MAP and data bursts via T-CID1 (1036).At RS1, the bursts are decapsulated and sent to the MS via its MS-CID(1038).

Since this handover is to a VBS in a different MMR tree, it may requireASN anchor point involvement (FIG. 15, 616). Furthermore, since thetarget VBS is in a different MMR tree, the serving VBS BS1 may send anMOB-BSHO-RSP message to the MS to force the MS to adopt a new CID, toensure no CID conflict in the MS's new tree.

RS Mobility

In FIG. 23 there is shown an RS (RS3) that moves intra-tree. The MSremains attached to RS3 during this process, and is unaware of thehandover. Prior to handover, the MMR topology is shown on the left. A BS1100 is coupled via one branch to an RS 1 (1102), and via another branchto an RS2 (1104) and RS3 (1106). The MS 1108 is attached to the RS31106. After handover, the MS 1108 is attached to the RS1 1102. Theworking flow for this process is shown in FIGS. 24A and 24B. Prior tohandover, there are four VBS's: VBS0 (BS), VBS1 (VBS0, RS1), VBS2 (VBS0,RS2), and VBS3 (VBS2, RS3). The VBS routing table for the BS includespath entries for all four VBS and their associated T-CID (T-CID 1-3respectively). RS1's VBS routing table 1112 a includes the path entryfor VBS1, and associated T-CID 1. The VBS routing table 1114 a for RS2includes the path list for VBS2 and its associated T-CID2, and the pathlist for VBS3 and its associated T-CID3. The VBS routing table 1114 afor RS3 includes the path list for VBS3, the associated T-CID3, and theassociated endpoint MS. The MS is shown currently attached to RS3 (1116a). DL-MAP and data bursts are relayed between the BS and MS via VBS3and T-CID3 (1120, 1122, 1124).

RS3 knows from its own VBS path list that its father is VBS2 (VBS0,RS2), which is its serving VBS. The BS broadcasts the MOB_NBR-ADVmessage, advertising other available VBSs including VBS0, VBS1, and VBS2(1126). RS3 starts its scan process with the recommended VBS list inthis advertisement message. Meanwhile, RS3 has received the DL-MAP fromRS1, which includes the VBS ID VBS1 (VBS0, RS1) (1128). RS3 uses thisVBSID for initial ranging. MOB_HO-REQ and MOB_HO-RSP messages areexchanged between RS3 and BS (1130). RNG-REQ and RNG-RSP messages areexchanged between RS3 and VBS1 (1132, 1134, 1136, 1138). The rangingprocess between RS3 and RS1 results in updates to the VBS routingtables. A new VBS VBS4 is created (via the same mechanisms as previouslydescribed) with path list (VBS1, RS3), and a new tunnel CID T-CID4. TheBS routing table 1110 b and the RS1 routing table 1112 b are updatedwith this new VBS4. RS3 then sends MOB_HO-IND to the BS indicating thatit is severing itself from the serving VBS1 (1140, 1142). Then DSD-REQand DSD-RSP messages are exchanged between BS and RS2 (1144, 1146) inorder to remove the VBS3 and T-CID3 from the RS2 routing table (1114 b),effectively eliminating VBS3. The BS then sends either a REG-RSP messageto RS1 and RS3 to force a T-CID update, or it exchanges DSAx messagesresulting in a new T-CID4 assigned to VBS4 (1148). The RS1 routing table1112 c and RS3 routing table 1116 b are updated with the T-CID4. The BSnow re-directs data flow to the MS (now attached to VBS4 (1118 b)) viathe new VBS4 by putting the new VBS4 T-CID4 in its DL-MAP and databursts. Data is thus relayed from BS to RS1 to RS3 via T-CID4. At RS3,the bursts are decapsulated and sent to the MS via it's CID, which hasnot changed.

In FIG. 25, there is shown an RS that moves intra-tree. Two MMR treesare shown. In their initial topologies as shown at the top of FIG. 21,BS1 (1200) is the root of one tree, and RS1 (1202) is subordinate to it.BS2 (1204) is the root of another tree, and RS2 (1206) is subordinate toit. An MS 1208 is initially attached to the RS1. There are four VBS—VBS0(BS2), VBS1 (VBS0, RS2), VBS2 (BS1), and VBS3 (VBS2, RS1). At the bottomof FIG. 21, the MMR topologies are shown after RS1 moves to attach toVBS0. Now BS1 has no children, while BS2 has two branches. A new VBS4includes BS2 and RS1, while VBS3 has been eliminated. The MS 1208remains attached to RS 1.

The work flow diagram for this handover is shown in FIGS. 26A-26B.Initially, the BS2 VBS routing table 1210 a has entries for VBS0 andVBS1. The VBS1 entry has associated with it T-CID1. The RS2 VBS routingtable 1212 a has an entry for VBS1 and T-CID1. The BS1 VBS routing table1214 a has entries for VBS2, and VBS3 and its T-CID2. The RS1 VBSrouting table 1216 a has an entry for VBS3, its T-CID2, and endpoint MS.The MS is attached to VBS3 (as indicated by 1218 a), and DL-MAP and databursts are exchanged between BS1 and MS via T-CID2 (1220, 1222).

BS1 and BS2 exchange their VBS routing tables so that each BS canadvertise VBS's for the other's subordinate trees as well as its own(1224). This exchange may involve ASN anchor point involvement. BS1sends its MOB_NBR-ADV message, which is received by RS1 (1226). Theadvertisement message includes BSI's recommended VBS list, includingBS2's VBS0 and VBS1. MOB_HO-REQ and M)B_HO-RSP messages are exchangedbetween BS1 and MS (1228). The RS1 has also received the DL-MAP fromVBS0 (1230). RS1 performs initial ranging with VBS0 by exchangingRNG-REQ and RNG RSP messages with VBS0 (1232, 1234). This results inupdates to the BS2 and RS1 tables adding VBS4 with path (VBS0, RS1).After RS1 sends MOB_HO-IND to the severing BS1 (1236), REG-RESP or DSAxmessages are exchanged between BS2 and RS1 (1238) resulting in theaddition of tunnel CID T-CID3 to the VBS4 entries in the respectivetables (1210 c, 1216 c). A further REG-RSP is sent from the BS2 to theMS in order to update the MS's CID (herein shown updated to CIDn) toensure no CID conflict between the separate MMR trees (1240). Now MS isattached to VBS4 (1218 b), and DL-MAP and data bursts are exchangedbetween the new BS2 and the MS via RS1 over T-CID3. Numerousmodifications and variations of the present invention are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the invention may be practisedotherwise than as specifically described herein.

1-14. (canceled)
 15. Apparatus for use in a wireless multi-hop relaynetwork arranged in a tree topology, the apparatus comprising: a firstvirtual access point (VAP) having a tree topology, wherein a tree headof the tree topology includes a base station, the tree topology of thefirst VAP including one or more VAP relay stations coupled to the basestation via subordinate tree branches; a second VAP having a treetopology, wherein a tree head of the tree topology includes a relaystation, the tree topology of the second VAP including one or more VAPrelay stations coupled to the relay stations via subordinate treebranches; the first and second VAPs associated as a first virtual basestation (VBS), the first and second VAPs each having a unique virtualbase station identifier (VBS-ID) associated with a path defined by thebase station and one or more VAP relay stations in at least one of thefirst and second VAPs in the first VBS; a VAP relay station in thesecond VAP having logic for using the VBS-ID of the second VAP forcommunicating with a subscriber station attached to the second VAP suchthat communications between the base station and the subscriber stationoccur via the first VBS, wherein a relay station in the first VBScomprises logic to perform the following functions: receive a DL-MAPmessage from the base station; a. if the relay station is not attachedto an upstream station then: send a range request message to theupstream station; receive a range response message from the upstreamstation containing a unique VBS-ID for the relay station; exchange DSxmessages with the upstream station to obtain a tunnel connectionidentifier (T-CID); and update a routing table associated with the relaystation with an entry including the VBS-ID and the T-CID; b. if therelay station is attached to an upstream station: replace the stationidentifier in the DL-MAP message with the VBS-ID for the relay station;and forward the DL-MAP message downstream.
 16. The apparatus of claim15, wherein the logic further perform the functions: receive a rangerequest message from a downstream relay station; receive a rangeresponse message from an upstream station containing a unique VBS-ID forthe downstream relay station; receive a DSx messages from the upstreamstation containing a T-CID for the downstream station; forward the Dsxmessage to the downstream station; updating, by the relay station, therouting table with the VBS-ID and T-CID for the downstream station. 17.The apparatus of claim 15, wherein the base station and all VAP relaystations in the first VAP share the same radio resource, and wherein thefirst VAP provides multiple radio links via the VAP relay stations; therelay station in the second VAP capable of communicating with the firstVAP over any one of the radio links in a manner transparent to the relaystation.
 18. The apparatus of claim 17, wherein the base station selectsthe radio link for communication with the relay station based on linksignal quality.
 19. The apparatus of claim 17, wherein the relay stationand all VAP relay stations in the second VAP share the same radioresource, and wherein the second VAP provides multiple second radiolinks via the VAP relay stations in the second VAP; the subscriberstation capable of communicating with the second VAP over any one of thesecond radio links in a manner transparent to the subscriber station.20. The apparatus of claim 19, wherein the relay station selects theradio link for communication with the subscriber station based on linksignal quality.
 21. The apparatus of claim 21, wherein the first VBS isassociated with the T-CID, and wherein the base station in the treetopology of the first VAP uses the T-CID to relay subscriber stationdata communications between the base station and the relay station inthe second VAP.
 22. The apparatus of claim 21, wherein the base stationin the first VAP and the relay station in the second VAP each comprise arouting table, each routing table including one or more entriescomprising: a VBS-ID, a path list associated with the VBS-ID, a T-CIDassociated with the virtual base station, an inter-VAP next hop, anintra-VAP next hop, an ingress port, an egress port, and an endpointidentifier.
 23. A method for use in a wireless multi-hop relay networkarranged in a tree topology, the method comprising the steps of:providing a first virtual access point (VAP) having a tree topology,wherein a tree head of the tree topology includes a base station, thetree topology of the first VAP including one or more VAP relay stationsa coupled to the base station via subordinate tree branches; providing asecond VAP having a tree topology, wherein a tree head of the treetopology includes a relay station and one or more VAP relay stationscoupled to the relay station via subordinate tree branches; associatingthe first and second VAPs as a first virtual base station (VBS), thefirst and second VAPs each having a unique virtual base stationidentifier (VBS-ID) associated with a path defined by the base stationand one or more VAP relay stations in at least one of the first andsecond VAPs in the first VBS; a VAP relay station in the second VAPusing the VBS-ID of the second VAP for communicating with a subscriberstation attached to the second VAP such that communications between thebase station and the subscriber station occur via the first VBS;receiving, by the relay station, a DL-MAP message from the base station;a. if the relay station is not attached to an upstream station then:sending a range request message to the upstream station; receiving arange response message from the upstream station containing a uniqueVBS-ID for the relay station; exchanging DSx messages with the upstreamstation to obtain a T-CID; updating, by the relay station, a routingtable with an entry including the VBS-ID and tunnel CID; b. if the relaystation is attached to an upstream station: replacing the stationidentifier in the DL-MAP message with the VBS-ID for the relay station;and using, by the last relay station in the branch, the VBS-IDassociated with the last relay station to communicate with an attachedsubscriber station such that communications between the base station andthe subscriber station occur via the first VBS.
 24. The method of claim23, further comprising: receiving, by the relay station, a range requestmessage from a downstream relay station; receiving, by the relaystation, a range response message from an upstream station containing aunique VBS-ID for the downstream relay station; receiving, by the relaystation, a DSx messages from the upstream station containing a T-CID forthe downstream station; forwarding, by the relay station, the Dsxmessage to the downstream station; and updating, by the relay station,the routing table with the VBS-ID and T-CID for the downstream station.25. A method for use in a wireless multi-hop relay network arranged in atree topology, the method comprising the steps of: providing a firstvirtual access point (VAP) having a tree topology, wherein a tree headof the tree topology includes a base station, the tree topology of thefirst VAP including one or more VAP relay stations coupled to the basestation via subordinate tree branches; providing a second VAP having atree topology, wherein a tree head of the tree topology includes a relaystation and one or more VAP relay stations coupled to the relay stationsvia subordinate tree branches; associating the first and second VAPs asa first virtual base station (VBS), the first and second VAPs eachhaving a unique virtual base station identifier (VBS-ID) associated witha path defined by the base station and one or more VAP relay stations inat least one of the first and second VAPs in the first VBS; using, by aVAP relay station in the second VAP, the VBS-ID of the second VAP forcommunicating with a subscriber station attached to the second VAP suchthat communications between the base station and the subscriber stationoccur via the first VBS; associating a second base station and one ormore relay stations along a single tree branch subordinate to the secondbase station as a second VBS; exchanging, by the first and second basestations, routing tables between the first and second base stations;sending, by the second base station, an advertisement message includinga list of available virtual base stations including the second virtualbase station; receiving, by the second base station, a handoverindication message from a subscriber station indicating that subscriberstation communications are transferring to the second VBS; updating, bythe second base station, a routing table in the second base station, toindicate a VBS-ID and a tunnel connection identifier (T-CID) for thesecond virtual base station to be used for communicating with thesubscriber station; updating, by each relay station in the secondvirtual base station, each respective relay station routing tables toindicate a VBS-ID and T-CID to be used for communicating with thesubscriber station; and updating the routing table in the first basestation to indicate that the first virtual base station and associatedT-CID are no longer used for communicating with the subscriber station.26. The method of claim 25, further comprising: updating the first basestation routing table to remove the VBS-ID and T-CID for the firstvirtual base station; and updating in each relay station in the firstvirtual base station the respective routing tables to remove the VBS-IDand T-CID for the first virtual base station.